They were driven by the hope of success, and the hope of what good fortunes would come to them, and all the dwarven people if they were to succeed. Very heroic, deep and noble motives IMO, not just simply money, wealth and greed. But also glory, vengeance and a greater good for all the Dwarvish peoples and possibly their old friends: the descendants of the kingdom of Dale. (I doubt it much that they also had in mind the rest of middle-earth, but maybe they did!) "I would draw some of the great tales in fullness, and leave many only placed in the scheme, and sketched. The cycles should be linked to a majestic whole, and yet leave scope for other minds and hands, wielding paint and music and drama"